Non GM Herbicide-Tolerant Rice Produced by Gene Targeting

A group of Japanese scientists reported the production of hybrid rice line tolerant to the herbicide bispyribac. Bispyribac (BS) is known to inhibit acetolactate synthase (ALS), the enzyme that catalyzes an early stage in the biosynthesis of branched amino acids like leucine, isoleucine and valine. ALS-inhibiting herbicides, which also comprise sulfonylureas and imidazolinones, control a broad spectrum of grass and broadleaf weeds, including weeds that are closely related to the crop itself. These herbicides remain an essential part of the multi-billion dollar weed control market because of their high selectivity, potency even at low applications, and non-toxicity to animals.

The group demonstrated that BS tolerance was due to two point mutations in the als gene, with the second point substitution responsible for increased tolerance. Employing their gene targeting system, they were able to regenerate plants harboring the two point mutations exclusively, without any foreign DNA insertion. The plants obtained are therefore equivalent to non-GM herbicide-tolerant rice plants generated by conventional breeding approaches that depend on spontaneous mutations.

Their gene targeting system proved to be more advantageous than chimeric DNA/RNA nucleotides, also able to introduce a single point mutation at a time. This is currently being used to induce site-specific changes in several plant species. Likewise, it might be a powerful tool in obtaining plants with agronomically valuable phenotypes such as salt tolerance and pigmentation, since many of these phenotypes are caused by single trait, or by a small number of point mutations.

For details, the paper published by the Plant Journal can be accessed by subscribers at http://www.blackwell-synergy.com/doi/full/10.1111/j.1365-313X.2007.03230.x